THE EM WAVELENGTH SCALE

To illustrate the range of EM wavelengths, we use a logarithmic scale. The logarithmic scale is needed because the range is so great that a linear scale is impractical. The left-hand portion of Fig. 1 is such a logarithmic scale that shows wavelengths from 108 m down to 10^-12 m. Each division, in the direction of shorter wavelength, represents a 100-fold decrease, or two orders of magnitude. Utility ac is near the top of this scale; the wavelength of 60-Hz ac in free space is quite long. The gamma rays are denoted approximately at the bottom; their EM wavelengths are tiny. It is apparent here that visible light takes up only a tiny sliver of the EM spectrum. In the right-hand scale, visible wavelengths are denoted in nanometers (nm).

Fig. 1. The EM spectrum from wavelengths of 10⁸ m down to 10^-12 m, and an exploded view of the visible-light spectrum within.